The screenwriter Dan Gilroy is on the phone, speaking about his brother Tony. Together, they wrote “The Bourne Legacy,” the storied, hotly anticipated fourth installment of the “Bourne” series based on the books by Robert Ludlum.

Director Tony Gilroy.

Tony Gilroy also directed “The Bourne Legacy,” which opened Aug. 10. That fact wouldn’t be news — the stakes of which his brother speaks wouldn’t be so high — were it not for the fractious and circuitous road it took to get him there. “The history of the franchise has been so shambolic over the years,” Tony Gilroy said recently from his home in New York. “I wasn’t about to be committed to anything ‘Bourne.’ ”

The back story: Tony Gilroy wrote or co-wrote all three “Bourne” films, which starred Matt Damon as the amnesiac assassin Jason Bourne. The first film in the series, “The Bourne Identity,” was directed by Doug Liman, whose managerial style was so chaotic that the franchise’s parent studio, Universal, barred him from making future installments. “The Bourne Supremacy” and “The Bourne Ultimatum” were directed by Paul Greengrass, who along with Damon fiddled with the idea of a fourth movie before dropping it altogether. (At one point Greengrass joked about calling it “The Bourne Redundancy.”)

When it was announced in 2010 that Gilroy would be directing the fourth “Bourne” film — without the title character — Damon responded in a fit of pique, noting that no one had called him with the news; he then let slip during a GQ interview that Gilroy — whom he had championed when Liman threatened to fire the writer from the first film — had phoned in the script for “The Bourne Ultimatum.” (Damon later contacted the magazine to apologize.)

With so much drama and so many fiery egos swirling around the “Bourne” franchise — which has grossed nearly $1 billion worldwide — it’s a wonder that Gilroy, 55, has volunteered to confront once again the beast he helped create.

“It’s perpetually astonishing to me,” he said of his return to the series. “It just does no good to get into the history of all this stuff, which is one chapter away from being a book long after everybody’s dead. I can only say it’s been a highly entertaining, very painful, very profitable, very wild ride.”

Gilroy signed on to “The Bourne Legacy” after his brother Dan asked him to have coffee with representatives of Ludlum’s estate, with whom Dan had been working. “I didn’t want to be rude,” Gilroy recalled, so he sat down with them. The problem, as Gilroy saw it, was that “you could never replace Matt as Jason Bourne. This isn’t James Bond. You can’t do a prequel. You can’t do any of those kinds of things, because there was never any cynicism attached to the franchise, and that was the one thing they had to hang on to.”

After the meeting, he recalled, he phoned his brother in California and said, “ ‘They’re really screwed. The only thing you can do is say there’s a larger conspiracy.’ And Dan said, ‘You ought to tell them that idea.’ ”

Gilroy did, and wound up creating a 30-page treatment about an agent named Aaron Cross who, like Bourne, is managed by a shadowy military-intelligence-security contractor cabal trying to construct perfect human fighting machines. (Gilroy made the directing gig part of his screenwriting deal on the film.) “The Bourne Legacy,” which stars Jeremy Renner as Cross, overlaps with the last Jason Bourne film, “The Bourne Ultimatum,” placing Cross and Bourne in the same conceptual universe.

It’s a stroke of brilliance, but one that necessitated Gilroy actually watching “The Bourne Ultimatum,” which he had never seen. “I finished the [‘Ultimatum’] script, handed it in and three weeks later I went into ‘Clayton,’ ” he said, referring to the 2007 legal thriller starring George Clooney. A taut, superbly constructed throwback to the lean urban dramas of the 1970s, “Michael Clayton” is considered by many critics and fans to be one of the best movies of its decade. Gilroy followed it up with “Duplicity,” a more lighthearted crime caper starring Julia Roberts and Clive Owen that recalled such Stanley Donen confections as “Charade” and “Two For the Road.”

Both “Michael Clayton” and “Duplicity” harkened a return to style and sophistication for a medium awash in spectacle and sequels. But both were made for adult audiences, a niche that, while narrow at the time, has shrunk to a barely perceptible sliver as far as Hollywood is concerned.

“The kind of movies I thought I would be making when I did ‘Clayton’ is over,” Gilroy said. “It’s gone, like beach erosion.” The good news, he quickly adds, is that “it’s just blasted off like crazy on television. American television right now is the most extraordinary offering of smart storytelling and acting that the American public’s ever been offered. But in general, it’s not a healthy part of the movie business, and I don’t think it’s going to get any healthier over time.”

Gilroy says this without rancor or bitterness. “Tony’s an absolute realist,” says his brother Dan. (A third brother, John, edited “The Bourne Legacy,” just as he has edited all of Tony’s movies.) “He understands the business as it stands now, and the marketplace. He just tries to make the best movie he can, and his philosophy would be that the box office follows.. . . It’s an extremely successful formula for him, and for anybody.”

For Tony’s part, he doesn’t know what will come next. “I have no script sitting here that I’m planning on doing.” What about getting the band back together and doing “Bourne” No. 5? “The Bourne Legacy” pointedly makes room for Jason to return, should Damon feel compelled. Gilroy sighs. “I’m so tired, the idea of doing this again is really incomprehensible.”

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